Use clock_settime to implement settimeofday.

Unconditionally, on all ports, use clock_settime to implement
settimeofday.  Remove sysdeps/unix/clock_settime.c, which implemented
clock_settime by calling settimeofday; new OS ports must henceforth
provide a real implementation of clock_settime.

Hurd had a real implementation of settimeofday but not of
clock_settime; this patch converts it into an implementation of
clock_settime.  It only supports CLOCK_REALTIME and microsecond
resolution; Hurd/Mach does not appear to have any support for
finer-resolution clocks.

The vestigial "set time zone" feature of settimeofday complicates the
generic settimeofday implementation a little.  The only remaining uses
of this feature that aren't just bugs, are using it to inform the
Linux kernel of the offset between the hardware clock and UTC, on
systems where the hardware clock doesn't run in UTC (usually because
of dual-booting with Windows).  There currently isn't any other way to
do this.  However, the callers that do this call settimeofday with
_only_ the timezone argument non-NULL.  Therefore, glibc's new
behavior is: callers of settimeofday must supply one and only one of
the two arguments.  If both arguments are non-NULL, or both arguments
are NULL, the call fails and sets errno to EINVAL.

When only the timeval argument is supplied, settimeofday calls
__clock_settime(CLOCK_REALTIME), same as stime.

When only the timezone argument is supplied, settimeofday calls a new
internal function called __settimezone.  On Linux, only, this function
will pass the timezone structure to the settimeofday system call.  On
all other operating systems, and on Linux architectures that don't
define __NR_settimeofday, __settimezone is a stub that always sets
errno to ENOSYS and returns -1.

The settimeoday syscall is enabled on Linux by the flag
COMPAT_32BIT_TIME, which is an option to either 32-bits ABIs or COMPAT
builds (defined usually by 64-bit kernels that want to support 32-bit
 ABIs, such as x86).  The idea to future 64-bit time_t only ABIs
is to not provide settimeofday syscall.

The same semantics are implemented for Linux/Alpha's GLIBC_2.0 compat
symbol for settimeofday.

There are no longer any internal callers of __settimeofday, so the
internal prototype is removed.

Checked on x86_64-linux-gnu, i686-linux-gnu, powerpc64le-linux-gnu,
powerpc64-linux-gnu, powerpc-linux-gnu, and aarch64-linux-gnu.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Reviewed-by: Lukasz Majewski <lukma@denx.de>

1 files changed, 24 insertions, 0 deletions

diff --git a/NEWS b/NEWS
index 8727b5e..b066c75 100644
--- a/NEWS
+++ b/NEWS
@@ -34,6 +34,30 @@ Deprecated and removed features, and other changes affecting compatibility:
   binaries and it has been removed from <time.h> header.  This function
   has been deprecated in favor of clock_settime.
 
+* The settimeofday function can still be used to set a system-wide time
+  zone when the operating system supports it.  This is because the Linux
+  kernel reused the API, on some architectures, to describe a system-wide
+  time-zone-like offset between the software clock maintained by the kernel,
+  and the "RTC" clock that keeps time when the system is shut down.
+
+  However, to reduce the odds of this offset being set by accident,
+  settimeofday can no longer be used to set the time and the offset
+  simultaneously.  If both of its two arguments are non-null, the call
+  will fail (setting errno to EINVAL).
+
+  Callers attempting to set this offset should also be prepared for the call
+  to fail and set errno to ENOSYS; this already happens on the Hurd and on
+  some Linux architectures.  The Linux kernel maintainers are discussing a
+  more principled replacement for the reused API.  After a replacement
+  becomes available, we will change settimeofday to fail with ENOSYS on all
+  platforms when its 'tzp' argument is not a null pointer.
+
+  Note that settimeofday itself is obsolescent according to POSIX.
+  Programs that set the system time should use clock_settime and/or
+  the adjtime family of functions instead.  We may also cease to make
+  settimeofday available to newly linked binaries after there is a
+  replacement for Linux's time-zone-like offset API.
+
 Changes to build and runtime requirements:
 
   [Add changes to build and runtime requirements here]